It turns out to be not all that easy to give a good description of what Ilsaluntë Valion is, or indeed what gnosis is. The words sometimes get in the way. Myth itself seems to be the best way to communicate gnostic concepts, but for the time being this prose will have to do

Over the years we have had several "Charter" and FAQ documents in which we tried to define what we do and, oftentimes more important, what we don't do.
These documents tended to expand, which is understandable, because if something is difficult to explain, you try harder and harder until they eventually became too lengthy for their intended purpose: people did not read them anymore.
Hence, this three-stage approach: there's a short README.1ST introduction, a more detailed longer introduction (which you are reading now), and we are now in the process of reworking the old Charter and FAQ documents into an in-depth explanation of the points discussed here (and more).

What is Ilsaluntë Valion?

Note especially that the essence of gnosis is not any specific conviction or set of writings or what have you; it pertains first of all to the way in one acquires experience or knowledge. You can also define it as opposed to "belief": gnosis does not come through believing, but through experiencing.
Although most of what you will find when looking for "gnosis" or "gnosticism" will relate more or less to the Judeo-Christian culture, though it contradicts a number of core values and accepted scripture. Here you can find a good general introduction by Dr. Stephan Hoeller.

So, how does it work? Apparently it is a fairly common thing to believe something. But it seems to be much less common to have a gnostic experience. It is by definition an individual thing; it cannot be transferred from one person to another; you cannot simply "accept" gnosis as people can do with faith.
The experience of acquiring gnosis is oftentimes compared to "finding a road or entrance" into a certain realm or area of experience. This realm is known by many different names: Tolkien named it Faerie, Jung named it the Collective Unconscious, some call it the Imaginal Realm. They all mean the same thing.
One gains entry to this place by way of the imagination. Don't take this as a frivolous statement though: it is not simply "any fantasy" that might float before your mind's eye. It is something much deeper than that, and it can take a serious, sustained effort to go there.
For Tolkien, this was his continued concentration on "creating" a language; for Jung, it was picturing himself as digging a hole in the ground, ever deeper, and deeper, and deeper.
Until something happened. At a given moment, elements turn up that appear not to be of their own making. This is an important characteristic, and found in all such experiences. Tolkien always had the idea of "discovering what was already out there, somewhere; not of 'making something up' "

What unites us here is that we are all touched by a peculiar quality found in Tolkien's writings; and we think that this is because of the nature of Tolkien's experience in Faerie. In his own words: it is clear that the Fairy Gold that he brought back from his travels did not turn to withered leaves. It still has the subtle, magic flavour of that country.
You could say that Ilsaluntë Valion is a place where we want to study this and who knows, maybe retrace Tolkien's steps into that realm - as far as is given to us. And if we should, to also bring back whatever we find there.

By now you may think that this Faerie is just another word for - well, someone's particularly fanciful imagination. This is not so. Everyone who has ever had this experience, or even someone who hasn't experienced it, but seriously contemplates someone else's experience knows that this is not the case. There is something very profound happening when you enter that realm. It is not something made up, a gilded lie. In fact, those who have ventured into that land can confirm that it is more real than our everyday, factual, physical world.
Those who have had such an experience know that Faerie may not be a fact, but it is very real. I am aware that this sounds strange or even crazy. It directly attacks the common consensus view of reality. But it can not be denied that there are truths that are not factual.

What do we do?
As stated above, gnosis is a very individual thing. The way in which it may (or may not) be achieved, the kind of experience, the intensity. It all depends on factors that are highly personal.

At the time of writing, there seem to be three major fields of interest. It's a categorisation that may hold now, but that doesn't mean that there could not be other ways. For the sake of this document I have called them roads here.

The (sub-)creative road
You could see this as the road of Tolkien himself. However meditation is also used here, the motivational force behind this road comes from the process of creating something - drawing, writing, whatever. When based on the gnostic impulse, this tends to bind you more closely to the imaginal realm. It is a self-amplifying process: the creative act brings you closer to Faerie, which in its turn will inspire you to create further. The "venturing into Faerie" may, or may not occur simultaneously with the creative labour: for Tolkien it seems that his linguistic 'meditations' were also his 'travelling agent', so to speak. But it seems also possible to separate them in time.
Next to exploring this imaginal world and becoming more conscious of one's personal existence within that realm, individuals who prefer this road have a strong impulse to also to "bring back some of the Fairie Gold" to the factual world and therewith enrich it. In essence this means "to act as an imtermediairy agent" between the two realms. These people do not seem to be motivated by wanting to understand the nature or workings of the relationship between the realms.

The ritualistic road
Rituals, possibly combined with meditations, are another way into the Imaginal. You can establish a close relationship with nature and the Moon cycle this way, by carrying out rituals and meditations specifically written for certain dates. They are linked with the Legendarium by following the Eldarin calendar and by dedicating the rituals to a specific Vala. There are also a couple of specific Eldarin holidays that can be observed.
Individuals on this road can be motivated by a search to improve balance and (spiritual) well-being. It also seems to strengthen the ability to travel to Fairie.

The research road
This pertains to the more experimental approach. Entheogens, when applied wisely, can be very helpful; as well as elements from other traditions that seem compatible with Gnosis, like animism. The overall goal is to gain more understanding of Mytho-History: how the Imaginal and factual worlds interweave and interrelate. In contrast to the sub-creative road above, individuals with this motivation might want to share their experiences and findings as well - albeit in different form (e.g. rather a document than a painting).

As with all categorisations, this one is arbitrary and just meant to illustrate some differences between roads you could take.
They are not mutually exclusive: someone with a strong liking for rituals could also be very active on the sub-creative road.